Base station apparatus and packet transmission method

ABSTRACT

A first scheduler  152  carries out scheduling deciding a destination apparatus based on radio line quality prediction results from a radio line quality prediction section  107.  A second scheduler  153  carries out scheduling on a time slot to which a packet to be retransmitted is assigned by the first scheduler  152,  based on the radio line quality prediction results from the radio line quality prediction section  107  and the scheduling results of the first scheduler  152.  A transmission control section  155  controls a transmission queue  156,  an error correction encoding section  158  and a modulation section  159,  in accordance with the scheduling results of the first scheduler  152  when a signal is an ACK signal, and in accordance with the scheduling results of the second scheduler  153  when the signal is a NACK signal. In this way, even when a transmitted packet is correctly demodulated, other packet can be transmitted in the time slot to which a packet to be retransmitted is assigned, so that decrease in the transmission rate can be prevented.

TECHNICAL FIELD

The present invention relates to a base station apparatus and packettransmission method for carrying out a downlink high-speed packettransmission.

BACKGROUND ART

There has been developed a downlink high-speed packet transmissionscheme (HSDPA, etc.) where a plurality of communication terminalapparatuses share a high-speed and large-capacity downlink channel and ahigh-speed packet transmission is carried out. In this transmissionscheme, a scheduling technique and an adaptive modulation technique havebeen used in order to enhance a transmission rate.

The scheduling technique is a technique in which a base stationapparatus sets a communication terminal apparatus (hereinafter referredto as a “destination apparatus”) serving as a downlink high-speed packetdestination for each time slot and assigns a packet to be transmitted toa destination apparatus. Further, the adaptive modulation technique is atechnique in which a base station apparatus determines a modulationmethod or an error correction encoding scheme adaptively depending on astate of a propagation path of a communication terminal apparatus towhich a packet is transmitted.

The base station apparatus predicts line quality in each communicationterminal apparatus for each time slot of one frame, determines as adestination apparatus a communication terminal apparatus with the bestline quality, and assigns to each time slot a packet to the destinationapparatus. Then, the base station apparatus subjects the packet to errorcorrection encoding and modulation according to information indicatingscheduling results and a scheme determined by scheduling, and transmitsthe packet to the destination apparatus.

Based on the information indicating received scheduling results, eachcommunication terminal apparatus carries out demodulation in a time slotto which the packet addressed to its own station is assigned, andcarries out CRC detection, etc. When packet data can be correctlydemodulated, the communication terminal apparatus transmits an ACKsignal indicating this result to the base station apparatus, whereaswhen packet data cannot be correctly demodulated, the communicationterminal apparatus transmits an NACK signal indicating this result tothe base station apparatus.

When receiving the NACK signal, the base station apparatus retransmitsthe previously transmitted packet in the time slot to which the packetis assigned by the scheduling. However, when the number of times forretransmission reaches the maximum number of times for retransmissionpreviously set in the system, the relevant packet is discarded and a newpacket is transmitted.

In a conventional scheduling method, however, when a transmitted packetis correctly demodulated in the destination apparatus and is notrequired to be retransmitted, subsequent time slots are not used, and asa result,a transmission rate is decreased.

DISCLOURE OF INVENTION

The object of the present invention is to provide a base stationapparatus and a packet transmission method, where even when atransmitted packet is correctly demodulated, other packet can betransmitted in a time slot to which a packet to be retransmitted isassigned, so that decrease in transmission rate can be prevented.

This object is achieved by preparing two schedulers to transmit a packetassigned by any one of schedulers, based on the decision resultsindicating whether or not retransmission of the previously transmittedpacket is necessary.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of a base stationapparatus according to one embodiment of the present invention,

FIG. 2 is a view showing one example of a scheduling in a firstscheduler according to one embodiment of the present invention, and

FIG. 3 is a view showing one example of a scheduling in a secondscheduler according to one embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are described in detail below byreferring to the accompanying drawings.

PREFERRED EMBODIMENT

FIG. 1 is a block diagram showing a configuration of a base stationapparatus according to one embodiment of the present invention. In FIG.1, the base station apparatus comprises an antenna 101, a duplexer 102,a reception RF section 103, a demodulation section 104, an errorcorrection decoding section 105, a separation section 106 and a radioline quality prediction section 107. The base station apparatus furthercomprises a user decision section 151, a first scheduler 152, a secondscheduler 153, a first multiplexing section 154, a transmission controlcircuit 155, a transmission queue 156, a second multiplexing section157, an error correction encoding section 158, a modulation section 159and a transmission RF section 160.

The duplexer 102 outputs a signal received by the antenna 101 to thereception RF section 103. Further, the duplexer 102 radio-transmits,from the antenna 101, a signal outputted from the transmission RFsection 160.

The reception RF section 103 converts a radio-frequency received signaloutputted from the duplexer 102 into a baseband digital signal, andoutputs it to the demodulation section 104.

The demodulation section 104 is provided as many as the number of thecommunication terminal apparatuses which carry out radio communication,carries out demodulation processing on the received baseband signal, andoutputs the resulting signal to the error correction decoding section105. The error correction decoding section 105 is provided as many asthe number of the communication terminal apparatuses which carries outradio communication, carries out error correction decoding processingsuch as Viterbi decoding on the demodulated signal, and outputs theresulting signal to the separation section 106.

The separation section 106 is provided as many as the number of thecommunication terminal apparatuses which carries out radiocommunication, separates an ACK signal or a NACK signal from the decodedsignal, and outputs it to the transmission control section 155. Inaddition, the separation section 106 separates a report value from thedecoded signal, and outputs it to the radio line quality predictionsection 107. Incidentally, the report value measured in thecommunication terminal apparatus is a value indicating the state of apropagation path between each relevant communication terminal apparatusand the base station apparatus.

The radio line quality prediction section 107 predicts the quality ofone-frame radio line in all the communication terminal apparatuses basedon the report value from each communication terminal apparatus, andoutputs the prediction results to the first scheduler 152 and the secondscheduler 153.

Based on the user information contained in a header of transmission datain each communication terminal apparatus, the user decision section 151decides that the relevant transmission data are to be used fortransmission to which user (communication terminal apparatus), andoutputs the decision results to the first scheduler 152 and the secondscheduler 153.

The first scheduler 152 refers to the decision results of the userdecision section 151, and carries out scheduling deciding a destinationapparatus based on the radio line quality prediction results from theradio line quality prediction section 107. In general, the firstscheduler 152 assigns the communication terminal apparatus with the bestline quality in each time slot. Further, the first scheduler 152 outputsinformation indicating the scheduling results to the second scheduler153, the first multiplexing section 154 and the transmission controlsection 155.

The second scheduler 153 refers to the decision results of the userdecision section 151, and carries out scheduling on the time slot towhich a packet to be retransmitted is assigned by the first scheduler152, based on the radio line quality prediction results from the radioline quality prediction section 107 and the scheduling results of thefirst scheduler 152. In that case, the second scheduler 153 assigns acommunication terminal apparatus with the best line quality except forthe communication terminal apparatus assigned by the first scheduler152. Further, the second scheduler 153 outputs the informationindicating the scheduling results to the first multiplexing section 154and the transmission control section 155.

Incidentally, the schedulings of the first scheduler 152 and the secondscheduler 153 will be detailed later.

The first multiplexing section 154 multiplexes the informationindicating the destination apparatus outputted from the first scheduler152 and the information indicating the destination apparatus outputtedfrom the second scheduler 153, and outputs the resulting information tothe second multiplexing section 157.

When inputting an ACK signal, the transmission control section 155instructs the transmission queue 156 to transmit new data. On the otherhand, when inputting a NACK signal, the transmission control section 155instructs the transmission queue 156 to retransmit the previouslytransmitted data. Further, the transmission control section 155 outputsthe information indicating a modulation method and an encoding rate tothe second multiplexing section 157, the error correction encodingsection 158 and the modulation section 159, based on the schedulingresults of the first scheduler 152 and the second scheduler 153.

The transmission queue 156 selects data to the destination apparatusinstructed by the transmission control section 155. On that occasion,when receiving an instruction to transmit new data, the transmissionqueue 156 deletes the stored data and outputs new data to the secondmultiplexing section 157, while storing the new data. On the other hand,when receiving an instruction to retransmit the previously transmitteddata, the transmission queue 156 outputs the stored data to the secondmultiplexing section 157.

The second multiplexing section 157 multiplexes the informationindicating the modulation method and encoding rate outputted from thetransmission control section 155 on the data outputted from thetransmission queue 156. The error correction encoding section 158subjects the output signal of the multiplexing section 157 to errorcorrection encoding according to the encoding rate scheme selected bythe transmission control section 155, and outputs the resulting signalto the modulation section 159. The modulation section 159 modulates theoutput signal of the error correction encoding section 158 according tothe modulation method selected by the transmission control section 155,and outputs the resulting signal to the transmission RF section 160.

The transmission RF section 160 converts a baseband digital signaloutputted from the modulation section 159 into a radio-frequency signal,and outputs the resulting signal to the duplexer 102.

The schedulings of the first scheduler 152 and the second scheduler 153are described in detail below.

FIG. 2 is a view showing one example of the scheduling of the firstscheduler 152. Further, FIG. 3 is a view showing one example of thescheduling of the second scheduler 153. In the columns of the main userin FIG. 2 and FIG. 3, “A, B, C . . . ” express destination apparatuses,“(1), (2), (3), . . . ” express the number of packets to be transmittedto the relevant destination apparatuses and “

” expresses retransmission.

As shown in FIG. 2, the first scheduler 152 carries out schedulingdeciding the destination apparatus, the packet to be transmitted, themodulation scheme and the encoding rate for each time slot of one frame.For example, FIG. 2 shows that the first scheduler 152 carries outscheduling such that a first packet is transmitted to a destinationapparatus “A” by a 64 QAM modulation system and a ¾ encoding rate in atime slot 1.

The second scheduler 153 carries out scheduling deciding the destinationapparatus, the packet to be transmitted, the modulation system and theencoding rate for the time slot to which the first scheduler 152 hasassigned a packet to be retransmitted. In FIG. 2, packets to beretransmitted are assigned to time slots 4, 6, 7 and 8. Accordingly, thesecond scheduler 153 carries out the scheduling only for these timeslots, as shown in FIG. 3.

The first multiplexing section 154 multiplexes the informationindicating scheduling results of the first scheduler 152 and the secondscheduler 153 as shown in FIG. 2 and FIG. 3, and outputs the resultinginformation to the second multiplexing section 157.

The transmission control section 155 controls the transmission queue156, the error correction encoding section 158 and the modulationsection 159 in accordance with the scheduling results of the firstscheduler 152 as shown in FIG. 2 when a signal inputted from theseparation section 106 is an ACK signal, and in accordance with thescheduling results of the second scheduler 153 as shown in FIG. 3 whenthe signal is a NACK signal.

For example, when inputting an ACK signal in the time slot 4 in FIG. 2and FIG. 3, the transmission control section 155 instructs thetransmission queue 156 to transmit a second packet addressed to acommunication terminal apparatus “B”, and outputs information indicatinga 16 QAM modulation system and a ¾ encoding rate to the secondmultiplexing section 157, the error correction encoding section 158 andthe modulation section 159.

Thus, by providing two schedulers to transmit a packet assigned by anyone of schedulers based on the decision results indicating whether ornot retransmission of the previously transmitted packet is necessary,even when the transmitted packet is correctly demodulated, other packetcan be transmitted in the time slot to which a packet to beretransmitted is assigned.

As is clear from the above descriptions, according to the presentinvention, even when a transmitted packet is correctly demodulated,other packet can be transmitted in a time slot to which a packet to beretransmitted is assigned, so that decrease in the transmission rate canbe prevented.

This application is based on Japanese Patent Application No. 2002-091206filed on Mar. 28, 2002, entire content of which is incorporated byreference herein.

Industrial Applicability

The present invention is suitable for use in a base station apparatus ina radio communication system for carrying out a downlink high-speedpacket transmission.

FIG. 1

-   101 ANTENNA-   102 DUPLEXER-   103 RECEPTION RF SECTION-   104 DEMODULATION SECTION-   105 ERROR CORRECTION DECODING SECTION-   106 SEPARATION SECTION-   107 RADIO LINE QUALITY PREDICTION SECTION-   151 USER DECISION SECTION-   152 FIRST SCHEDULER-   153 SECOND SCHEDULER-   154 FIRST MULTIPLEXING SECTION-   155 TRANSMISSION CONTROL SECTION-   156 TRANSMISSION QUEUE-   157 SECOND MULTIPLEXING SECTION-   158 ERROR CORRECTION ENCODING SECTION-   159 MODULATION SECTION-   160 TRANSMISSION RF SECTION-   RECEPTION SIGNAL-   TRANSMISSION SIGNAL    FIG. 2-   TIME SLOT-   MAIN USER-   MODULATION SYSTEM-   ENCODING RATE    FIG. 3-   TIME SLOT-   SUB USER-   MODULATION SYSTEM-   ENCODING RATE-   NONE

1. A base station apparatus comprising: a line quality predictionsection for predicting radio line quality in each communication terminalapparatus based on a report value indicating the state of a propagationpath, a first scheduler for carrying out scheduling of determining acommunication terminal apparatus as a packet destination in each timeslot based on prediction results of this line quality predictionsection, a second scheduler for carrying out scheduling of determining acommunication terminal apparatus as a packet destination in the timeslot to which a packet to be retransmitted is assigned in said firstscheduler, based on the prediction results of said line qualityprediction section, and a transmission section for transmitting a packetin accordance with the scheduling of said first scheduler or said secondscheduler.
 2. The base station apparatus as claimed in claim 1, whereinthe first scheduler assigns a communication terminal apparatus with thebest line quality in each time slot, and said second scheduler assigns acommunication terminal apparatus with the best line quality except forthe communication terminal apparatus assigned in said first scheduler.3. The base station apparatus as claimed in claim 1, wherein thetransmission section transmits the packet in the time slot to which thepacket to be retransmitted is assigned, in accordance with thescheduling of the first scheduler when retransmission is required fromthe communication terminal apparatus to which the packet has beentransmitted, or in accordance with the scheduling of the secondscheduler when no retransmission is required.
 4. A packet transmissionmethod comprising: a step of carrying out a first scheduling ofdetermining a communication terminal apparatus as a packet destinationin each time slot based on prediction results of radio line quality ineach communication terminal apparatus, a step of carrying out a secondscheduling of determining a preliminary communication terminal as apacket destination in a time slot to which a packet to be retransmittedis assigned, and a step of transmitting a packet in accordance with saidfirst scheduler or said second scheduler.
 5. The packet transmissionmethod as claimed in claim 4, further comprising transmitting the packetin the time slot to which the packet to be retransmitted is assigned, inaccordance with the scheduling of the first scheduler whenretransmission is required from the communication terminal apparatus towhich the packet has been transmitted, and in accordance with thescheduling of the second scheduler when no retransmission is required.